High-resolution sequence stratigraphy and reservoir differences between the southern and northern culminations in the third member of the Feixianguan Formation in the Jiannan structure,Hubei

Sequence stratigraphic division is conducted on the strata of the Jian-45 and Jian-42 wells at the southern and northern culminations in the Jiannan structure using the Exxon’s classic sequence stratigraphic model.These strata may be divided into four Ⅱ-type fourth-order sequences.A sequence stratigraphic correlation is made for the southern and northern culminations,respectively.The oolitic shoals in the southern culmination were developed in the highstand systems tract of Sequences 1,2 and 3,whereas those at the northern culmination were developed during the transgressive period of Sequences 4.The former may be defined as the "highstand shoals",whereas the latter may be defined as the "transgressive shoals" whose reservoir capability is poor due to the lack of surface solution.The bedded dolostone reservoirs at the northern culmination were developed in the upper highstand systems tract of Sequences 3,and horizontally occur between the oolitic shoals and micritic limestone.In these cases,rolling stepout drilling and deviated drilling are proposed to improve production at the southern culmination,whereas at the northern culmination,high-quality dolostone reservoirs are expected.